Onions (Allium cepa)

Onion is herbaceous biennial plant of the family Alliaceae family grown as an annual.
The leaf bases swell to form the underground mature edible bulbs. Onions are pungent; because they contain a sulfur-rich volatile oil. Peeling or slicing them can bring tears to a person’s eyes. Onions vary in size, shape, colour, and pungency. Though low in standard nutrients, they are valued for their flavour. Spring/bunching onions, scallions and green onions are grown especially for their green tops.

Ecological Requirement
Altitude
Onions do well in medium to high altitudes of 500-2000m. It grows best at altitude below 1,900m.
Rainfall
The crop requires well distributed rainfall of between 500-700mm during the growing season and fairly long dry period for ripening.
Temperature
Most varieties prefer relatively warm conditions, but some are tolerant to higher
temperatures. The optimum temperature for production is 15-300C. Onions require a relatively long dry period for ripening.
Soils
Onions grow well in fertile, well drained, fertile loams with a high level of organic matter and good water holding capacity. The optimum pH should be about 6.0-7.0.